1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a wireless mesh network, and more particularly to, a method of transferring information on a station to nodes in a wireless mesh network when the station joins or leaves a mesh access point.
2. Description of the Related Art
The standardization of a wireless mesh network that is an extension of a wireless local area network (LAN) relating to the IEEE 802.11s standards are being discussed. A consortium of companies is proposing a hybrid wireless mesh protocol (HWMP) as a routing protocol to be used in the wireless mesh network. This working group is collectively known as the Simple, Efficient and Extensible Mesh (SEEMesh) group.
The HWMP is a hybrid protocol that uses a proactive routing protocol and a reactive routing protocol together. Using the reactive routing protocol, nodes do not always maintain a routing table of a network, but instead, search a routing path to a destination node until a source node is ready to transmit data. Using the proactive routing protocol, nodes always maintain the routing table. The HWMP uses an ad hoc on-demand distance vector routing (AODV) protocol as the reactive routing protocol.
FIG. 1 is a diagram for searching for a path using the AODV protocol in a wireless mesh network. Referring to FIG. 1, if node A searches for the path for transmitting data to node D, the node A writes an address of the node A in a source address field and an address of the node D in a destination address field of a route requirement (RREQ) packet and broadcasts the RREQ packet. If Node B, which receives the RREQ packet, recognizes that node A is searching for the path to node D, node B registers with a routing table that the node B is one hop from node A based on a hop count field of the RREQ packet, and then broadcasts the RREQ packet.
Node C, which receives the RREQ packet from node B, registers with a routing table that node B is a next hop for the path to the node A, and then broadcasts the RREQ packet.
If node D, which receives the RREQ packet from node C, recognizes that the RREQ packet is transmitted to the node D according to the destination address of the RREQ packet, then node D generates a route response (RREP) packet having node A as its destination, transmits the RREP packet to the node C via unicast, and registers node C in a precursor list of an address of the node D.
Then node C, which receives the RREP packet from node D, finds through the routing table that the node B is the next hop for the path to the node A, transmits the RREP packet to the node B via unicast, and registers the node B in a precursor list of node D. Likewise, node B transmits the received RREP packet to the node A and registers node A in the precursor list of node D, thereby searching for the path between the node A and the node D.
The precursor list is used when a link between nodes is disconnected or no more paths are searched. For example, if node C recognizes that node C and the node D are disconnected, then node C determines node D as a destination node and informs nodes communicating with node C of the fact, which is performed for node C to transmit a route error (RERR) packet to nodes registered with the precursor list of node D in the routing table of node C. As described above, since node B is registered in the precursor list of node D in the routing table of node C, based on this fact, node C transmits the RERR packet to the node B, and then node B, which received the RERR packet, also transmits the REPP packet to the node A registered in the precursor list of the node D, so that all nodes that have the node D as the destination node receive the RERR packet and recognize that the path between all nodes and the node D is disconnected.
FIG. 2 is a diagram for explaining a related art method of forwarding information on a station when the station moves. Referring to FIG. 2, it is assumed that nodes A through I are mesh access points that comprise an access point function and an ad-hoc routing function in accord with 802.11.
When station 1 moves from a service area of mesh access point J to an area of mesh access point G, the mesh access point J recognizes that the station 1 is out of the service area of the mesh access point J and transmits an RERR packet to nodes registered in a precursor list of station 1 as described with reference to FIG. 1. For example, if node A and node C communicate with the station 1, all nodes between the node A and node J and all nodes between the node C and the node J over a path receive the RERR packet.
The RERR packet must be transmitted to nodes whenever a hand-off of a station occurs. If stations very frequently move in a wireless mesh network, hand-offs occur frequently. In particular, if a lot of stations exist in the wireless mesh network, the RERR packet is frequently used due to hand-offs or link disconnections, consuming network resources.
Also, the existing HWMP standards do not clearly describe how a root node and other mesh access points can recognize that the station 1 newly joins the service area of the mesh access point G.